In this episode, we'll explore the gripping story of how the structure of DNA was discovered, a tale filled with perseverance, luck, and a hint of betrayal.
Learn about the key figures in this scientific breakthrough, including the crucial but often overlooked role of Rosalind Franklin, and discover how understanding DNA's double helix shape has transformed modern science and medicine.
[00:00:05] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English.
[00:00:12] The show where you can listen to fascinating stories and learn weird and wonderful things about the world at the same time as improving your English.
[00:00:21] I'm Alastair Budge, and today is part two of our mini-series on the theme of “scientific discovery”.
[00:00:29] In part one, we talked about the invention of the leap year and ideas throughout history about how to manage our calendars.
[00:00:38] Next up, in part three, we’ll talk about maths and some of the unusual and surprising ways in which mathematical discoveries changed the world.
[00:00:48] And in today’s episode, part two, we are going to talk about the discovery of the structure of DNA.
[00:00:55] It is a fantastic story of perseverance, luck, sexism, betrayal, and a quest to solve one of life’s most important and fundamental questions.
[00:01:07] So, let’s not waste a minute and get right into it.
[00:01:13] The House of Habsburg was one of the most longstanding and powerful European noble families.
[00:01:20] Starting in the 11th century in modern-day Austria, the family went to rule over modern-day Hungary, Croatia, Portugal, Spain, much of Italy, and, lest I forget, the position of Holy Roman Emperor for a whopping 300 years.
[00:01:39] This great expansion of power did not come about primarily through military conquest but through marriage. Daughters and sons were married off to other European royalty, and by the 15th century or so, Habsburgs could be found in almost every major European royal court.
[00:02:02] And, being a royal family, fathers were unwilling to let their children marry anyone of a lower social rank, which inevitably meant that young princes and princesses would end up marrying their cousins, some more and some less distant.
[00:02:22] This led to a curious phenomenon in the royal houses of Europe: the Habsburg jaw, or the Habsburg lip, as it’s sometimes known.
[00:02:33] Essentially, it is a condition where the lower jaw is significantly longer, and it sticks out, the lower lip is often enlarged, and there is a crossbite, where the lower teeth are further out than the upper teeth.
[00:02:51] It is a phenomenon that is clearly visible in the portraits of many of the Habsburg family members, perhaps most famously Charles II of Spain.
[00:03:01] In fact, most commentators believe that their jaws would actually have been far more enlarged than the official portraits because the artist would have wanted to flatter them, to make them seem less prominent than they really were.
[00:03:18] Such phenomena are common when there are high levels of interbreeding, where people who are closely related have children, and certain characteristics become particularly pronounced in these children.
[00:03:32] Of course, the fact that children typically share some similarities with their parents is no “new” discovery.
[00:03:40] For as long as humans have existed and have reproduced, it has been clear that something is passed from parent to child, and whatever this is, it can govern everything from the colour of their hair to the colour of their skin to the shape of their face to non-physical traits, like temperament or intelligence.
[00:04:04] You probably look a little bit like your parents. If you have children, they probably look a bit like you. Clearly, some information is passed from parent to child.
[00:04:17] But for most of human history, no one really knew how this “information” was passed down.
[00:04:26] What was the mechanism?
[00:04:28] What was it that parents gave to their children that determined these traits?
[00:04:33] Where was this information stored?
[00:04:36] And what explained how children weren’t an exact replica of their parents?
[00:04:43] Why were some characteristics passed from parent to child and others weren’t?
[00:04:49] These questions puzzled scientists and philosophers for centuries.
[00:04:55] Some thought it was related to blood—hence the term “bloodline.”
[00:05:01] Others believed in a mystical “essence” that passed from one generation to the next.
[00:05:08] But no one had any concrete evidence to explain the biological process.
[00:05:16] Fast forward to the 19th century, and a series of discoveries started to shed light on this mystery.
[00:05:25] It began with a monk named Gregor Mendel, a German man often called the father of genetics.
[00:05:34] Mendel’s experiments with pea plants in the 1850s and 1860s revealed that traits like flower colour or seed shape followed predictable patterns when passed from one generation to another.
[00:05:50] For example, if a purebred yellow pea plant reproduced with a purebred green pea plant, it would produce yellow, not green pea plants.
[00:06:02] But in subsequent generations, green pea plants could still appear, even if the plants they came from were both yellow.
[00:06:12] It was unlikely, only occurring in a ratio of 1 green to 3 yellow, but the green “characteristic”, whatever it was, it didn’t disappear completely; it was still there, somewhere.
[00:06:28] If this is bringing back memories of high school biology class, yes, this is because yellow is dominant, and green is recessive, in pea plants at least.
[00:06:39] He didn’t know it at the time, but Mendel was describing how genes worked—units of information that control traits.
[00:06:49] But where were these “genes” located?
[00:06:54] Mendel’s work didn’t answer that question, and for decades, it was largely ignored.
[00:07:01] It wasn’t until 1869 that a Swiss scientist named Friedrich Miescher made an accidental discovery that would eventually help answer this question.
[00:07:14] While studying white blood cells, he found a strange substance inside their nuclei.
[00:07:21] He called it “nuclein,” and it was what we now know as DNA.
[00:07:28] Yet, at the time, no one knew what this mysterious substance did.
[00:07:35] Most scientists believed it was just some kind of cellular waste, and indeed, towards the end of his life, Miescher rejected the possibility that this nuclein had anything to do with genes, saying that it was, and I’m quoting directly, “irrelevant to inheritance”.
[00:07:55] So, while scientists had started to gather clues about heredity—traits passed from parent to child—they were still none the wiser about the details.
[00:08:07] What exactly carried this genetic information, and how did it work?
[00:08:13] Now, let’s jump to the early 20th century.
[00:08:18] By this time, scientists knew that cells had a nucleus, and they suspected that the nucleus contained something important for heredity, for inheritance.
[00:08:30] But what that “something” was remained a mystery.
[00:08:35] In the early 1900s, scientists discovered that chromosomes, thread-like structures in the nucleus, played a role in heredity.
[00:08:45] They noticed that chromosomes seemed to divide and duplicate when cells reproduced, and they thought chromosomes might carry the mysterious hereditary material.
[00:08:59] Chromosomes, as scientists observed, are made up of two main substances: proteins and something called DNA.
[00:09:10] At the time, most scientists believed that proteins, not DNA, were where this genetic information was stored.
[00:09:19] Proteins, with 20 different amino acids, seemed more complex and more capable of storing information.
[00:09:28] And DNA appeared quite simple—just a repetitive chain of four chemical bases.
[00:09:37] Perhaps perfectly reasonably, given the complexity of life, of all of the information that is required to reproduce another human, passing down characteristics from parent to child, most scientists believed that this genetic information was held in the more complicated-looking substance–proteins–not in DNA.
[00:10:00] But, as you will know, they were wrong.
[00:10:04] The first major clue that DNA was the molecule of heredity came from a series of experiments in the 1940s.
[00:10:14] In 1944, a team of scientists led by a man named Oswald Avery performed an experiment that showed that DNA, not proteins, carried genetic information.
[00:10:28] Avery and his colleagues studied bacteria that caused pneumonia, and they demonstrated that DNA from one type of bacteria could change, or “transform,” another type into something completely different.
[00:10:44] This was revolutionary, but many scientists were still sceptical.
[00:10:51] It seemed too strange that such a simple molecule could carry the vast amount of information needed to create a living organism.
[00:11:01] By the early 1950s, the scientific community had started to come to a consensus that DNA was important, but still no one understood its structure.
[00:11:12] If scientists could figure out the shape of DNA, they believed they could unlock the secret of how it worked and, therefore, truly understand the blueprint to human life.
[00:11:27] This sparked fierce competition among scientists to solve the puzzle.
[00:11:33] And this is where the story takes a more dramatic turn.
[00:11:38] At King’s College in London, a brilliant scientist named Rosalind Franklin was using a cutting-edge technique called X-ray crystallography to study DNA.
[00:11:50] This method involved shining X-rays at a crystal of DNA and analyzing the pattern of how the rays scattered. Franklin’s work was meticulous, and she produced the clearest images of DNA ever seen, including one particularly famous image known as Photo 51.
[00:12:14] Photo 51 was groundbreaking because, although it didn’t show the complete structure, it provided clear evidence that DNA had a helical structure, like a twisty snake or a spiral staircase.
[00:12:31] The X-ray diffraction pattern showed repeating features that hinted at the molecule’s shape and its internal symmetry.
[00:12:41] This was an invaluable clue to determine not only what DNA looked like but also how it functioned.
[00:12:50] But Franklin wasn’t the only scientist at King’s College trying to unravel DNA’s mysteries.
[00:12:57] Another researcher there, Maurice Wilkins, was taking a rather different approach—and the two of them never truly hit it off.
[00:13:06] Part of the problem was a muddled start: the lab director hired Franklin while Wilkins was away on holiday and led her to believe that she would be the sole researcher focusing on DNA.
[00:13:21] When Wilkins returned, he assumed Franklin was a new assistant rather than a colleague on equal footing.
[00:13:29] She, in turn, resented that someone else was working on what she understood to be her exclusive project.
[00:13:38] From that point on, collaboration was replaced by competition, and the atmosphere between them remained tense.
[00:13:47] Despite their frosty relationship, they were both making important strides.
[00:13:53] Franklin continued to refine her X-ray crystallography techniques, while Wilkins pursued alternative methods for studying DNA’s structure.
[00:14:04] Had they worked together more smoothly, perhaps the story would have unfolded differently.
[00:14:11] Instead, a crucial piece of Franklin’s data would soon find its way into the hands of two men at Cambridge, sparking the final leg of the race to decipher the structure of DNA.
[00:14:25] While Wilkins and Franklin were working away at King's College London, 100 kilometres north, at Cambridge University, two young men were also trying to crack the code.
[00:14:38] Their names were Francis Crick and James Watson, and neither was a biologist by training.
[00:14:46] Crick was a physicist, and Watson, who had travelled to Cambridge from the United States, was a zoologist, an expert in the study of animals.
[00:14:57] And, while at King's College London, Franklin and Wilkins were taking photographs and conducting experiments, at Cambridge, Watson and Crick were trying to figure out the structure of DNA using a more theoretical approach.
[00:15:14] Key to this was the work of Franklin and Wilkins, and, in particular, Franklin’s famous Photo 51, the photo that showed that DNA had a helical structure.
[00:15:27] Now, there are varying accounts of what happened next.
[00:15:32] Some say that Wilkins showed Photo 51 to Watson and Crick without the permission of Rosalind Franklin.
[00:15:41] Other accounts suggest that Franklin did give permission.
[00:15:46] What is clear is that Watson and Crick were shown Photo 51, and this gave the pair the critical data they needed to solve the structure of DNA.
[00:15:58] The two young men rushed back to Cambridge and started to build models that could explain how the strands within DNA could fit inside the helix.
[00:16:10] And when I say model, this was literally a physical model, with the men cutting out different shapes and trying to place them together in a way that did not contradict the laws of chemistry.
[00:16:24] It did not take them particularly long.
[00:16:27] On a Saturday morning in 1953, Watson and Crick set to work building their physical model of DNA.
[00:16:36] Watson later said they solved the puzzle in just a few hours—like fitting together pieces of a jigsaw. The double helix structure was born, and instinctively, it made sense in a way that no other model had before, it was the first model of DNA’s structure that obeyed the laws of science.
[00:16:58] According to the legend, Francis Crick rushed into The Eagle pub in Cambridge and proclaimed that he and Watson had "found the secret of life".
[00:17:10] They had built the first accurate model of DNA in 1953: the famous double helix.
[00:17:17] The work was published a few months later, in the scientific journal Nature.
[00:17:23] The introduction contained perhaps one of science’s greatest understatements: “This structure has novel features which are of considerable biological interest.”
[00:17:36] And then “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."
[00:17:48] In other words, their model showed how genetic material can duplicate itself from parent to child.
[00:17:58] It was, to state the obvious, revolutionary.
[00:18:02] But not immediately.
[00:18:04] Crick and Watson had just proposed a model; it did seem to make perfect sense, but they hadn’t definitely proven anything. And indeed, this revolutionary paper was only 900 words long, with no experimental data.
[00:18:22] The next few years were followed with rigorous analysis by the scientific community, and their proposed structure stood up. It was correct, and in 1962 Crick, Watson and Wilkins jointly received the Nobel Prize.
[00:18:40] Rosalind Franklin, you will note, did not.
[00:18:45] Unfortunately, she had been diagnosed with cancer at the age of 36, and a year later, in 1958, four years before the men received the Nobel Prize, she died.
[00:18:58] The Nobel Prize cannot be awarded posthumously, it cannot be awarded to someone who is dead.
[00:19:06] And for a long time, Rosalind Franklin did not receive much recognition at all for her work on DNA, and all the credit went to Crick and Watson, with Wilkins getting the credit for the King’s College London part.
[00:19:21] She was written out of the story, in part because of her early death, but also because the men who did get the credit largely neglected to mention her.
[00:19:32] Of course, this is deeply unfair and has been used as yet another example of how women get a raw deal in the male-dominated world of scientific research, and how their often tireless work behind the scenes is written out of history.
[00:19:48] Thankfully, the contribution of Rosalind Franklin is now much more widely known, and even the Nature journal describes her work as “crucial to the discovery of the structure of DNA”.
[00:20:02] And the discovery of the structure of DNA, and therefore how DNA works, has touched a myriad of aspects of modern life.
[00:20:11] Over the following decades, scientists learned how to read the genetic code, sequence entire genomes, and even edit DNA.
[00:20:22] Today, the study of DNA is central to medicine, agriculture, and countless other fields.
[00:20:29] In the example of medicine, thanks to our understanding of DNA, doctors can now identify genetic mutations that cause diseases like cancer.
[00:20:39] This means treatments can be more targeted, focusing on what’s causing the disease at its core.
[00:20:46] And, to state the obvious, there is still a huge amount of work being done on better understanding and decoding the structure of DNA.
[00:20:55] One of the biggest breakthroughs came with the Human Genome Project, which mapped out all the genes in human DNA.
[00:21:03] And now, DNA sequencing—reading the genetic code—has become faster and cheaper.
[00:21:10] This is opening up exciting possibilities for the future.
[00:21:14] Imagine going to a doctor and getting a treatment that’s custom-made for you based on your unique DNA.
[00:21:22] Then there’s gene editing, with tools like CRISPR, which let scientists make precise changes to DNA. This could help us cure genetic diseases or even prevent them before they happen.
[00:21:37] Of course, it raises big ethical questions.
[00:21:41] Every parent wants their child to be happy and healthy, but should parents also be allowed to select traits like height, eye colour or even intelligence?
[00:21:52] Could this lead to a future where only the wealthy can ‘enhance’ their children’s DNA?"
[00:21:58] The potential is enormous, and it’s exciting and controversial in equal measure.
[00:22:04] DNA has been described as the “code of life,” and now, for the first time, we’re starting to learn how to read—and even write—that code.
[00:22:15] OK then, that is it for today's episode on DNA, the building blocks of life, and the long and fascinating journey to discover its structure.
[00:22:26] As a reminder, this was part two of our three-part mini-series on the theme of “scientific discovery”.
[00:22:33] In part one, we looked at leap years, and next up we will be learning about how mathematics changed the world.
[00:22:41] You've been listening to English Learning for Curious Minds by Leonardo English.
[00:22:46] I'm Alastair Budge, you stay safe, and I'll catch you in the next episode.
[00:00:05] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English.
[00:00:12] The show where you can listen to fascinating stories and learn weird and wonderful things about the world at the same time as improving your English.
[00:00:21] I'm Alastair Budge, and today is part two of our mini-series on the theme of “scientific discovery”.
[00:00:29] In part one, we talked about the invention of the leap year and ideas throughout history about how to manage our calendars.
[00:00:38] Next up, in part three, we’ll talk about maths and some of the unusual and surprising ways in which mathematical discoveries changed the world.
[00:00:48] And in today’s episode, part two, we are going to talk about the discovery of the structure of DNA.
[00:00:55] It is a fantastic story of perseverance, luck, sexism, betrayal, and a quest to solve one of life’s most important and fundamental questions.
[00:01:07] So, let’s not waste a minute and get right into it.
[00:01:13] The House of Habsburg was one of the most longstanding and powerful European noble families.
[00:01:20] Starting in the 11th century in modern-day Austria, the family went to rule over modern-day Hungary, Croatia, Portugal, Spain, much of Italy, and, lest I forget, the position of Holy Roman Emperor for a whopping 300 years.
[00:01:39] This great expansion of power did not come about primarily through military conquest but through marriage. Daughters and sons were married off to other European royalty, and by the 15th century or so, Habsburgs could be found in almost every major European royal court.
[00:02:02] And, being a royal family, fathers were unwilling to let their children marry anyone of a lower social rank, which inevitably meant that young princes and princesses would end up marrying their cousins, some more and some less distant.
[00:02:22] This led to a curious phenomenon in the royal houses of Europe: the Habsburg jaw, or the Habsburg lip, as it’s sometimes known.
[00:02:33] Essentially, it is a condition where the lower jaw is significantly longer, and it sticks out, the lower lip is often enlarged, and there is a crossbite, where the lower teeth are further out than the upper teeth.
[00:02:51] It is a phenomenon that is clearly visible in the portraits of many of the Habsburg family members, perhaps most famously Charles II of Spain.
[00:03:01] In fact, most commentators believe that their jaws would actually have been far more enlarged than the official portraits because the artist would have wanted to flatter them, to make them seem less prominent than they really were.
[00:03:18] Such phenomena are common when there are high levels of interbreeding, where people who are closely related have children, and certain characteristics become particularly pronounced in these children.
[00:03:32] Of course, the fact that children typically share some similarities with their parents is no “new” discovery.
[00:03:40] For as long as humans have existed and have reproduced, it has been clear that something is passed from parent to child, and whatever this is, it can govern everything from the colour of their hair to the colour of their skin to the shape of their face to non-physical traits, like temperament or intelligence.
[00:04:04] You probably look a little bit like your parents. If you have children, they probably look a bit like you. Clearly, some information is passed from parent to child.
[00:04:17] But for most of human history, no one really knew how this “information” was passed down.
[00:04:26] What was the mechanism?
[00:04:28] What was it that parents gave to their children that determined these traits?
[00:04:33] Where was this information stored?
[00:04:36] And what explained how children weren’t an exact replica of their parents?
[00:04:43] Why were some characteristics passed from parent to child and others weren’t?
[00:04:49] These questions puzzled scientists and philosophers for centuries.
[00:04:55] Some thought it was related to blood—hence the term “bloodline.”
[00:05:01] Others believed in a mystical “essence” that passed from one generation to the next.
[00:05:08] But no one had any concrete evidence to explain the biological process.
[00:05:16] Fast forward to the 19th century, and a series of discoveries started to shed light on this mystery.
[00:05:25] It began with a monk named Gregor Mendel, a German man often called the father of genetics.
[00:05:34] Mendel’s experiments with pea plants in the 1850s and 1860s revealed that traits like flower colour or seed shape followed predictable patterns when passed from one generation to another.
[00:05:50] For example, if a purebred yellow pea plant reproduced with a purebred green pea plant, it would produce yellow, not green pea plants.
[00:06:02] But in subsequent generations, green pea plants could still appear, even if the plants they came from were both yellow.
[00:06:12] It was unlikely, only occurring in a ratio of 1 green to 3 yellow, but the green “characteristic”, whatever it was, it didn’t disappear completely; it was still there, somewhere.
[00:06:28] If this is bringing back memories of high school biology class, yes, this is because yellow is dominant, and green is recessive, in pea plants at least.
[00:06:39] He didn’t know it at the time, but Mendel was describing how genes worked—units of information that control traits.
[00:06:49] But where were these “genes” located?
[00:06:54] Mendel’s work didn’t answer that question, and for decades, it was largely ignored.
[00:07:01] It wasn’t until 1869 that a Swiss scientist named Friedrich Miescher made an accidental discovery that would eventually help answer this question.
[00:07:14] While studying white blood cells, he found a strange substance inside their nuclei.
[00:07:21] He called it “nuclein,” and it was what we now know as DNA.
[00:07:28] Yet, at the time, no one knew what this mysterious substance did.
[00:07:35] Most scientists believed it was just some kind of cellular waste, and indeed, towards the end of his life, Miescher rejected the possibility that this nuclein had anything to do with genes, saying that it was, and I’m quoting directly, “irrelevant to inheritance”.
[00:07:55] So, while scientists had started to gather clues about heredity—traits passed from parent to child—they were still none the wiser about the details.
[00:08:07] What exactly carried this genetic information, and how did it work?
[00:08:13] Now, let’s jump to the early 20th century.
[00:08:18] By this time, scientists knew that cells had a nucleus, and they suspected that the nucleus contained something important for heredity, for inheritance.
[00:08:30] But what that “something” was remained a mystery.
[00:08:35] In the early 1900s, scientists discovered that chromosomes, thread-like structures in the nucleus, played a role in heredity.
[00:08:45] They noticed that chromosomes seemed to divide and duplicate when cells reproduced, and they thought chromosomes might carry the mysterious hereditary material.
[00:08:59] Chromosomes, as scientists observed, are made up of two main substances: proteins and something called DNA.
[00:09:10] At the time, most scientists believed that proteins, not DNA, were where this genetic information was stored.
[00:09:19] Proteins, with 20 different amino acids, seemed more complex and more capable of storing information.
[00:09:28] And DNA appeared quite simple—just a repetitive chain of four chemical bases.
[00:09:37] Perhaps perfectly reasonably, given the complexity of life, of all of the information that is required to reproduce another human, passing down characteristics from parent to child, most scientists believed that this genetic information was held in the more complicated-looking substance–proteins–not in DNA.
[00:10:00] But, as you will know, they were wrong.
[00:10:04] The first major clue that DNA was the molecule of heredity came from a series of experiments in the 1940s.
[00:10:14] In 1944, a team of scientists led by a man named Oswald Avery performed an experiment that showed that DNA, not proteins, carried genetic information.
[00:10:28] Avery and his colleagues studied bacteria that caused pneumonia, and they demonstrated that DNA from one type of bacteria could change, or “transform,” another type into something completely different.
[00:10:44] This was revolutionary, but many scientists were still sceptical.
[00:10:51] It seemed too strange that such a simple molecule could carry the vast amount of information needed to create a living organism.
[00:11:01] By the early 1950s, the scientific community had started to come to a consensus that DNA was important, but still no one understood its structure.
[00:11:12] If scientists could figure out the shape of DNA, they believed they could unlock the secret of how it worked and, therefore, truly understand the blueprint to human life.
[00:11:27] This sparked fierce competition among scientists to solve the puzzle.
[00:11:33] And this is where the story takes a more dramatic turn.
[00:11:38] At King’s College in London, a brilliant scientist named Rosalind Franklin was using a cutting-edge technique called X-ray crystallography to study DNA.
[00:11:50] This method involved shining X-rays at a crystal of DNA and analyzing the pattern of how the rays scattered. Franklin’s work was meticulous, and she produced the clearest images of DNA ever seen, including one particularly famous image known as Photo 51.
[00:12:14] Photo 51 was groundbreaking because, although it didn’t show the complete structure, it provided clear evidence that DNA had a helical structure, like a twisty snake or a spiral staircase.
[00:12:31] The X-ray diffraction pattern showed repeating features that hinted at the molecule’s shape and its internal symmetry.
[00:12:41] This was an invaluable clue to determine not only what DNA looked like but also how it functioned.
[00:12:50] But Franklin wasn’t the only scientist at King’s College trying to unravel DNA’s mysteries.
[00:12:57] Another researcher there, Maurice Wilkins, was taking a rather different approach—and the two of them never truly hit it off.
[00:13:06] Part of the problem was a muddled start: the lab director hired Franklin while Wilkins was away on holiday and led her to believe that she would be the sole researcher focusing on DNA.
[00:13:21] When Wilkins returned, he assumed Franklin was a new assistant rather than a colleague on equal footing.
[00:13:29] She, in turn, resented that someone else was working on what she understood to be her exclusive project.
[00:13:38] From that point on, collaboration was replaced by competition, and the atmosphere between them remained tense.
[00:13:47] Despite their frosty relationship, they were both making important strides.
[00:13:53] Franklin continued to refine her X-ray crystallography techniques, while Wilkins pursued alternative methods for studying DNA’s structure.
[00:14:04] Had they worked together more smoothly, perhaps the story would have unfolded differently.
[00:14:11] Instead, a crucial piece of Franklin’s data would soon find its way into the hands of two men at Cambridge, sparking the final leg of the race to decipher the structure of DNA.
[00:14:25] While Wilkins and Franklin were working away at King's College London, 100 kilometres north, at Cambridge University, two young men were also trying to crack the code.
[00:14:38] Their names were Francis Crick and James Watson, and neither was a biologist by training.
[00:14:46] Crick was a physicist, and Watson, who had travelled to Cambridge from the United States, was a zoologist, an expert in the study of animals.
[00:14:57] And, while at King's College London, Franklin and Wilkins were taking photographs and conducting experiments, at Cambridge, Watson and Crick were trying to figure out the structure of DNA using a more theoretical approach.
[00:15:14] Key to this was the work of Franklin and Wilkins, and, in particular, Franklin’s famous Photo 51, the photo that showed that DNA had a helical structure.
[00:15:27] Now, there are varying accounts of what happened next.
[00:15:32] Some say that Wilkins showed Photo 51 to Watson and Crick without the permission of Rosalind Franklin.
[00:15:41] Other accounts suggest that Franklin did give permission.
[00:15:46] What is clear is that Watson and Crick were shown Photo 51, and this gave the pair the critical data they needed to solve the structure of DNA.
[00:15:58] The two young men rushed back to Cambridge and started to build models that could explain how the strands within DNA could fit inside the helix.
[00:16:10] And when I say model, this was literally a physical model, with the men cutting out different shapes and trying to place them together in a way that did not contradict the laws of chemistry.
[00:16:24] It did not take them particularly long.
[00:16:27] On a Saturday morning in 1953, Watson and Crick set to work building their physical model of DNA.
[00:16:36] Watson later said they solved the puzzle in just a few hours—like fitting together pieces of a jigsaw. The double helix structure was born, and instinctively, it made sense in a way that no other model had before, it was the first model of DNA’s structure that obeyed the laws of science.
[00:16:58] According to the legend, Francis Crick rushed into The Eagle pub in Cambridge and proclaimed that he and Watson had "found the secret of life".
[00:17:10] They had built the first accurate model of DNA in 1953: the famous double helix.
[00:17:17] The work was published a few months later, in the scientific journal Nature.
[00:17:23] The introduction contained perhaps one of science’s greatest understatements: “This structure has novel features which are of considerable biological interest.”
[00:17:36] And then “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."
[00:17:48] In other words, their model showed how genetic material can duplicate itself from parent to child.
[00:17:58] It was, to state the obvious, revolutionary.
[00:18:02] But not immediately.
[00:18:04] Crick and Watson had just proposed a model; it did seem to make perfect sense, but they hadn’t definitely proven anything. And indeed, this revolutionary paper was only 900 words long, with no experimental data.
[00:18:22] The next few years were followed with rigorous analysis by the scientific community, and their proposed structure stood up. It was correct, and in 1962 Crick, Watson and Wilkins jointly received the Nobel Prize.
[00:18:40] Rosalind Franklin, you will note, did not.
[00:18:45] Unfortunately, she had been diagnosed with cancer at the age of 36, and a year later, in 1958, four years before the men received the Nobel Prize, she died.
[00:18:58] The Nobel Prize cannot be awarded posthumously, it cannot be awarded to someone who is dead.
[00:19:06] And for a long time, Rosalind Franklin did not receive much recognition at all for her work on DNA, and all the credit went to Crick and Watson, with Wilkins getting the credit for the King’s College London part.
[00:19:21] She was written out of the story, in part because of her early death, but also because the men who did get the credit largely neglected to mention her.
[00:19:32] Of course, this is deeply unfair and has been used as yet another example of how women get a raw deal in the male-dominated world of scientific research, and how their often tireless work behind the scenes is written out of history.
[00:19:48] Thankfully, the contribution of Rosalind Franklin is now much more widely known, and even the Nature journal describes her work as “crucial to the discovery of the structure of DNA”.
[00:20:02] And the discovery of the structure of DNA, and therefore how DNA works, has touched a myriad of aspects of modern life.
[00:20:11] Over the following decades, scientists learned how to read the genetic code, sequence entire genomes, and even edit DNA.
[00:20:22] Today, the study of DNA is central to medicine, agriculture, and countless other fields.
[00:20:29] In the example of medicine, thanks to our understanding of DNA, doctors can now identify genetic mutations that cause diseases like cancer.
[00:20:39] This means treatments can be more targeted, focusing on what’s causing the disease at its core.
[00:20:46] And, to state the obvious, there is still a huge amount of work being done on better understanding and decoding the structure of DNA.
[00:20:55] One of the biggest breakthroughs came with the Human Genome Project, which mapped out all the genes in human DNA.
[00:21:03] And now, DNA sequencing—reading the genetic code—has become faster and cheaper.
[00:21:10] This is opening up exciting possibilities for the future.
[00:21:14] Imagine going to a doctor and getting a treatment that’s custom-made for you based on your unique DNA.
[00:21:22] Then there’s gene editing, with tools like CRISPR, which let scientists make precise changes to DNA. This could help us cure genetic diseases or even prevent them before they happen.
[00:21:37] Of course, it raises big ethical questions.
[00:21:41] Every parent wants their child to be happy and healthy, but should parents also be allowed to select traits like height, eye colour or even intelligence?
[00:21:52] Could this lead to a future where only the wealthy can ‘enhance’ their children’s DNA?"
[00:21:58] The potential is enormous, and it’s exciting and controversial in equal measure.
[00:22:04] DNA has been described as the “code of life,” and now, for the first time, we’re starting to learn how to read—and even write—that code.
[00:22:15] OK then, that is it for today's episode on DNA, the building blocks of life, and the long and fascinating journey to discover its structure.
[00:22:26] As a reminder, this was part two of our three-part mini-series on the theme of “scientific discovery”.
[00:22:33] In part one, we looked at leap years, and next up we will be learning about how mathematics changed the world.
[00:22:41] You've been listening to English Learning for Curious Minds by Leonardo English.
[00:22:46] I'm Alastair Budge, you stay safe, and I'll catch you in the next episode.
[00:00:05] Hello, hello hello, and welcome to English Learning for Curious Minds, by Leonardo English.
[00:00:12] The show where you can listen to fascinating stories and learn weird and wonderful things about the world at the same time as improving your English.
[00:00:21] I'm Alastair Budge, and today is part two of our mini-series on the theme of “scientific discovery”.
[00:00:29] In part one, we talked about the invention of the leap year and ideas throughout history about how to manage our calendars.
[00:00:38] Next up, in part three, we’ll talk about maths and some of the unusual and surprising ways in which mathematical discoveries changed the world.
[00:00:48] And in today’s episode, part two, we are going to talk about the discovery of the structure of DNA.
[00:00:55] It is a fantastic story of perseverance, luck, sexism, betrayal, and a quest to solve one of life’s most important and fundamental questions.
[00:01:07] So, let’s not waste a minute and get right into it.
[00:01:13] The House of Habsburg was one of the most longstanding and powerful European noble families.
[00:01:20] Starting in the 11th century in modern-day Austria, the family went to rule over modern-day Hungary, Croatia, Portugal, Spain, much of Italy, and, lest I forget, the position of Holy Roman Emperor for a whopping 300 years.
[00:01:39] This great expansion of power did not come about primarily through military conquest but through marriage. Daughters and sons were married off to other European royalty, and by the 15th century or so, Habsburgs could be found in almost every major European royal court.
[00:02:02] And, being a royal family, fathers were unwilling to let their children marry anyone of a lower social rank, which inevitably meant that young princes and princesses would end up marrying their cousins, some more and some less distant.
[00:02:22] This led to a curious phenomenon in the royal houses of Europe: the Habsburg jaw, or the Habsburg lip, as it’s sometimes known.
[00:02:33] Essentially, it is a condition where the lower jaw is significantly longer, and it sticks out, the lower lip is often enlarged, and there is a crossbite, where the lower teeth are further out than the upper teeth.
[00:02:51] It is a phenomenon that is clearly visible in the portraits of many of the Habsburg family members, perhaps most famously Charles II of Spain.
[00:03:01] In fact, most commentators believe that their jaws would actually have been far more enlarged than the official portraits because the artist would have wanted to flatter them, to make them seem less prominent than they really were.
[00:03:18] Such phenomena are common when there are high levels of interbreeding, where people who are closely related have children, and certain characteristics become particularly pronounced in these children.
[00:03:32] Of course, the fact that children typically share some similarities with their parents is no “new” discovery.
[00:03:40] For as long as humans have existed and have reproduced, it has been clear that something is passed from parent to child, and whatever this is, it can govern everything from the colour of their hair to the colour of their skin to the shape of their face to non-physical traits, like temperament or intelligence.
[00:04:04] You probably look a little bit like your parents. If you have children, they probably look a bit like you. Clearly, some information is passed from parent to child.
[00:04:17] But for most of human history, no one really knew how this “information” was passed down.
[00:04:26] What was the mechanism?
[00:04:28] What was it that parents gave to their children that determined these traits?
[00:04:33] Where was this information stored?
[00:04:36] And what explained how children weren’t an exact replica of their parents?
[00:04:43] Why were some characteristics passed from parent to child and others weren’t?
[00:04:49] These questions puzzled scientists and philosophers for centuries.
[00:04:55] Some thought it was related to blood—hence the term “bloodline.”
[00:05:01] Others believed in a mystical “essence” that passed from one generation to the next.
[00:05:08] But no one had any concrete evidence to explain the biological process.
[00:05:16] Fast forward to the 19th century, and a series of discoveries started to shed light on this mystery.
[00:05:25] It began with a monk named Gregor Mendel, a German man often called the father of genetics.
[00:05:34] Mendel’s experiments with pea plants in the 1850s and 1860s revealed that traits like flower colour or seed shape followed predictable patterns when passed from one generation to another.
[00:05:50] For example, if a purebred yellow pea plant reproduced with a purebred green pea plant, it would produce yellow, not green pea plants.
[00:06:02] But in subsequent generations, green pea plants could still appear, even if the plants they came from were both yellow.
[00:06:12] It was unlikely, only occurring in a ratio of 1 green to 3 yellow, but the green “characteristic”, whatever it was, it didn’t disappear completely; it was still there, somewhere.
[00:06:28] If this is bringing back memories of high school biology class, yes, this is because yellow is dominant, and green is recessive, in pea plants at least.
[00:06:39] He didn’t know it at the time, but Mendel was describing how genes worked—units of information that control traits.
[00:06:49] But where were these “genes” located?
[00:06:54] Mendel’s work didn’t answer that question, and for decades, it was largely ignored.
[00:07:01] It wasn’t until 1869 that a Swiss scientist named Friedrich Miescher made an accidental discovery that would eventually help answer this question.
[00:07:14] While studying white blood cells, he found a strange substance inside their nuclei.
[00:07:21] He called it “nuclein,” and it was what we now know as DNA.
[00:07:28] Yet, at the time, no one knew what this mysterious substance did.
[00:07:35] Most scientists believed it was just some kind of cellular waste, and indeed, towards the end of his life, Miescher rejected the possibility that this nuclein had anything to do with genes, saying that it was, and I’m quoting directly, “irrelevant to inheritance”.
[00:07:55] So, while scientists had started to gather clues about heredity—traits passed from parent to child—they were still none the wiser about the details.
[00:08:07] What exactly carried this genetic information, and how did it work?
[00:08:13] Now, let’s jump to the early 20th century.
[00:08:18] By this time, scientists knew that cells had a nucleus, and they suspected that the nucleus contained something important for heredity, for inheritance.
[00:08:30] But what that “something” was remained a mystery.
[00:08:35] In the early 1900s, scientists discovered that chromosomes, thread-like structures in the nucleus, played a role in heredity.
[00:08:45] They noticed that chromosomes seemed to divide and duplicate when cells reproduced, and they thought chromosomes might carry the mysterious hereditary material.
[00:08:59] Chromosomes, as scientists observed, are made up of two main substances: proteins and something called DNA.
[00:09:10] At the time, most scientists believed that proteins, not DNA, were where this genetic information was stored.
[00:09:19] Proteins, with 20 different amino acids, seemed more complex and more capable of storing information.
[00:09:28] And DNA appeared quite simple—just a repetitive chain of four chemical bases.
[00:09:37] Perhaps perfectly reasonably, given the complexity of life, of all of the information that is required to reproduce another human, passing down characteristics from parent to child, most scientists believed that this genetic information was held in the more complicated-looking substance–proteins–not in DNA.
[00:10:00] But, as you will know, they were wrong.
[00:10:04] The first major clue that DNA was the molecule of heredity came from a series of experiments in the 1940s.
[00:10:14] In 1944, a team of scientists led by a man named Oswald Avery performed an experiment that showed that DNA, not proteins, carried genetic information.
[00:10:28] Avery and his colleagues studied bacteria that caused pneumonia, and they demonstrated that DNA from one type of bacteria could change, or “transform,” another type into something completely different.
[00:10:44] This was revolutionary, but many scientists were still sceptical.
[00:10:51] It seemed too strange that such a simple molecule could carry the vast amount of information needed to create a living organism.
[00:11:01] By the early 1950s, the scientific community had started to come to a consensus that DNA was important, but still no one understood its structure.
[00:11:12] If scientists could figure out the shape of DNA, they believed they could unlock the secret of how it worked and, therefore, truly understand the blueprint to human life.
[00:11:27] This sparked fierce competition among scientists to solve the puzzle.
[00:11:33] And this is where the story takes a more dramatic turn.
[00:11:38] At King’s College in London, a brilliant scientist named Rosalind Franklin was using a cutting-edge technique called X-ray crystallography to study DNA.
[00:11:50] This method involved shining X-rays at a crystal of DNA and analyzing the pattern of how the rays scattered. Franklin’s work was meticulous, and she produced the clearest images of DNA ever seen, including one particularly famous image known as Photo 51.
[00:12:14] Photo 51 was groundbreaking because, although it didn’t show the complete structure, it provided clear evidence that DNA had a helical structure, like a twisty snake or a spiral staircase.
[00:12:31] The X-ray diffraction pattern showed repeating features that hinted at the molecule’s shape and its internal symmetry.
[00:12:41] This was an invaluable clue to determine not only what DNA looked like but also how it functioned.
[00:12:50] But Franklin wasn’t the only scientist at King’s College trying to unravel DNA’s mysteries.
[00:12:57] Another researcher there, Maurice Wilkins, was taking a rather different approach—and the two of them never truly hit it off.
[00:13:06] Part of the problem was a muddled start: the lab director hired Franklin while Wilkins was away on holiday and led her to believe that she would be the sole researcher focusing on DNA.
[00:13:21] When Wilkins returned, he assumed Franklin was a new assistant rather than a colleague on equal footing.
[00:13:29] She, in turn, resented that someone else was working on what she understood to be her exclusive project.
[00:13:38] From that point on, collaboration was replaced by competition, and the atmosphere between them remained tense.
[00:13:47] Despite their frosty relationship, they were both making important strides.
[00:13:53] Franklin continued to refine her X-ray crystallography techniques, while Wilkins pursued alternative methods for studying DNA’s structure.
[00:14:04] Had they worked together more smoothly, perhaps the story would have unfolded differently.
[00:14:11] Instead, a crucial piece of Franklin’s data would soon find its way into the hands of two men at Cambridge, sparking the final leg of the race to decipher the structure of DNA.
[00:14:25] While Wilkins and Franklin were working away at King's College London, 100 kilometres north, at Cambridge University, two young men were also trying to crack the code.
[00:14:38] Their names were Francis Crick and James Watson, and neither was a biologist by training.
[00:14:46] Crick was a physicist, and Watson, who had travelled to Cambridge from the United States, was a zoologist, an expert in the study of animals.
[00:14:57] And, while at King's College London, Franklin and Wilkins were taking photographs and conducting experiments, at Cambridge, Watson and Crick were trying to figure out the structure of DNA using a more theoretical approach.
[00:15:14] Key to this was the work of Franklin and Wilkins, and, in particular, Franklin’s famous Photo 51, the photo that showed that DNA had a helical structure.
[00:15:27] Now, there are varying accounts of what happened next.
[00:15:32] Some say that Wilkins showed Photo 51 to Watson and Crick without the permission of Rosalind Franklin.
[00:15:41] Other accounts suggest that Franklin did give permission.
[00:15:46] What is clear is that Watson and Crick were shown Photo 51, and this gave the pair the critical data they needed to solve the structure of DNA.
[00:15:58] The two young men rushed back to Cambridge and started to build models that could explain how the strands within DNA could fit inside the helix.
[00:16:10] And when I say model, this was literally a physical model, with the men cutting out different shapes and trying to place them together in a way that did not contradict the laws of chemistry.
[00:16:24] It did not take them particularly long.
[00:16:27] On a Saturday morning in 1953, Watson and Crick set to work building their physical model of DNA.
[00:16:36] Watson later said they solved the puzzle in just a few hours—like fitting together pieces of a jigsaw. The double helix structure was born, and instinctively, it made sense in a way that no other model had before, it was the first model of DNA’s structure that obeyed the laws of science.
[00:16:58] According to the legend, Francis Crick rushed into The Eagle pub in Cambridge and proclaimed that he and Watson had "found the secret of life".
[00:17:10] They had built the first accurate model of DNA in 1953: the famous double helix.
[00:17:17] The work was published a few months later, in the scientific journal Nature.
[00:17:23] The introduction contained perhaps one of science’s greatest understatements: “This structure has novel features which are of considerable biological interest.”
[00:17:36] And then “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."
[00:17:48] In other words, their model showed how genetic material can duplicate itself from parent to child.
[00:17:58] It was, to state the obvious, revolutionary.
[00:18:02] But not immediately.
[00:18:04] Crick and Watson had just proposed a model; it did seem to make perfect sense, but they hadn’t definitely proven anything. And indeed, this revolutionary paper was only 900 words long, with no experimental data.
[00:18:22] The next few years were followed with rigorous analysis by the scientific community, and their proposed structure stood up. It was correct, and in 1962 Crick, Watson and Wilkins jointly received the Nobel Prize.
[00:18:40] Rosalind Franklin, you will note, did not.
[00:18:45] Unfortunately, she had been diagnosed with cancer at the age of 36, and a year later, in 1958, four years before the men received the Nobel Prize, she died.
[00:18:58] The Nobel Prize cannot be awarded posthumously, it cannot be awarded to someone who is dead.
[00:19:06] And for a long time, Rosalind Franklin did not receive much recognition at all for her work on DNA, and all the credit went to Crick and Watson, with Wilkins getting the credit for the King’s College London part.
[00:19:21] She was written out of the story, in part because of her early death, but also because the men who did get the credit largely neglected to mention her.
[00:19:32] Of course, this is deeply unfair and has been used as yet another example of how women get a raw deal in the male-dominated world of scientific research, and how their often tireless work behind the scenes is written out of history.
[00:19:48] Thankfully, the contribution of Rosalind Franklin is now much more widely known, and even the Nature journal describes her work as “crucial to the discovery of the structure of DNA”.
[00:20:02] And the discovery of the structure of DNA, and therefore how DNA works, has touched a myriad of aspects of modern life.
[00:20:11] Over the following decades, scientists learned how to read the genetic code, sequence entire genomes, and even edit DNA.
[00:20:22] Today, the study of DNA is central to medicine, agriculture, and countless other fields.
[00:20:29] In the example of medicine, thanks to our understanding of DNA, doctors can now identify genetic mutations that cause diseases like cancer.
[00:20:39] This means treatments can be more targeted, focusing on what’s causing the disease at its core.
[00:20:46] And, to state the obvious, there is still a huge amount of work being done on better understanding and decoding the structure of DNA.
[00:20:55] One of the biggest breakthroughs came with the Human Genome Project, which mapped out all the genes in human DNA.
[00:21:03] And now, DNA sequencing—reading the genetic code—has become faster and cheaper.
[00:21:10] This is opening up exciting possibilities for the future.
[00:21:14] Imagine going to a doctor and getting a treatment that’s custom-made for you based on your unique DNA.
[00:21:22] Then there’s gene editing, with tools like CRISPR, which let scientists make precise changes to DNA. This could help us cure genetic diseases or even prevent them before they happen.
[00:21:37] Of course, it raises big ethical questions.
[00:21:41] Every parent wants their child to be happy and healthy, but should parents also be allowed to select traits like height, eye colour or even intelligence?
[00:21:52] Could this lead to a future where only the wealthy can ‘enhance’ their children’s DNA?"
[00:21:58] The potential is enormous, and it’s exciting and controversial in equal measure.
[00:22:04] DNA has been described as the “code of life,” and now, for the first time, we’re starting to learn how to read—and even write—that code.
[00:22:15] OK then, that is it for today's episode on DNA, the building blocks of life, and the long and fascinating journey to discover its structure.
[00:22:26] As a reminder, this was part two of our three-part mini-series on the theme of “scientific discovery”.
[00:22:33] In part one, we looked at leap years, and next up we will be learning about how mathematics changed the world.
[00:22:41] You've been listening to English Learning for Curious Minds by Leonardo English.
[00:22:46] I'm Alastair Budge, you stay safe, and I'll catch you in the next episode.
